This invention relates to a movement sensor and relates particularly to a device for detecting movement or variations of movement of a body.
Movement sensors are used in a variety of applications. In some applications, the movement sensors are designed to detect movement in a predetermined direction. In other applications, the movement sensors are designed to detect movement in more than one direction. The present invention is directed particularly at omni-directional movement sensors and will be described with particular reference to the use of such a sensor in a motor vehicle security and alarm system.
Various forms of movement sensors are available. For example, a mercury switch is a form of movement sensor commonly used in motor vehicle alarm systems and which operates when mercury moves from an at-rest position due either to acceleration of the switch, resulting from vehicle movement, or tilting of the switch. However, the known movement sensors suffer a number of inherent disadvantages.
The mercury switch, for example, can be set to detect acceleration and movement from a horizontal plane. However, as the switch is reliant on the gravitational effect on the mercury, the switch will not necessarily function as designed if its operating attitude is not substantially horizontal.
Another type of movement sensor works on the pendulum principal, where movement causes a suspended magnet to swing above a xe2x80x9cHall Effectxe2x80x9d device thereby generating a signal in response to detected movement. A restriction with this sensor is that it only works on a horizontal plane.
Another known sensor uses a piezoelectric transducer wherein an acceleration or a sharp movement causes a piezoelectric material to generate an electrical signal. Even though this type of sensor is unaffected by its orientation, it is very susceptible to vibration but is not sensitive enough to detect small accelerations or slow variations in movement.
U.S. Pat. No 4,648,273 discloses a device for detecting the influence of gravitational forces on a flowable body contained within a cavity. The device is designed particularly for use in rocketry and space flight programming and instrumentation. However, the device is designed particularly to not only measure acceleration but to determine the state of zero gravity at which time the flowable material forms a sphere due to the surface tension of the medium.
Japanese Patent Abstract No 59-202067 (Mitsubishi Denki KK) discloses a three-axial direction acceleration detecting apparatus which includes a sphere supported by springs within a hollow container. Acceleration of the container causes the sphere to move relative thereto and that movement is detected by a light source on each of the yawing, rolling and pitching axes.
Japanese Patent Abstract No JP 6-258336 relates to an acceleration sensor which uses a liquid metal ball within a sphere. Shadows of the liquid ball are projected onto multi-element photo detectors. Acceleration causes the ball to deform in shape and the change in the shape of the shadow is measured as a function of the acceleration.
Japanese Patent Abstract No JP 6-258337 shows a sensor in which movement is detected by sensing changes to the size of the shadow of a ball within a sphere and detecting the shadow position using a multi-element photo detector.
It is therefore desirable to provide an improved movement sensor which has a number of applications but is particularly useful in motor vehicle security and alarm systems.
It is also desirable to provide a movement sensor which is able to detect movement in or variations in the motion of a body.
It is also desirable to provide a movement sensor which is relatively simple and economic to manufacture.
It is also desirable to provide a movement sensor which is reliable in operation.
According to one aspect of the invention there is provided a movement sensor including a chamber containing a spherical body freely movable within the chamber, radiation emitting means located relative to the chamber so that emitted radiation passes through the chamber, radiation detecting means to detect emitted radiation passing through the chamber, and signal generating means to generate a signal in response to detected radiation.
Preferably, the chamber is a spherical shape and has a relatively smooth inner surface which offers minimal resistance to movement of the spherical body within the chamber. If desired, the chamber may be evacuated, or partially evacuated, to further reduce resistance to movement of the body within the chamber.
The radiation emitting means may comprise a light source or a source of infra-red or any other suitable form of radiation including ultrasound. For simplicity, however, the invention will be described with reference to the radiation emitting means as a source of visible light.
The radiation detecting means preferably comprises a light detector which incorporates signal generating means so as to generate a signal proportional to the amount of detected light. Electrical circuitry is used to compare the output signal from the light detector with the input to the light source and detect any variation produced by movement of the body within the chamber which changes the amount of radiation passing through the chamber.
In one form of the invention, the chamber wall is formed of a material through which the radiation passes. Thus, the chamber may be formed of a synthetic plastics material which is transparent to the radiation. In a particular embodiment, the wall is formed of a material which is translucent to visible light but transparent to infra-red radiation.
In another form of the invention the chamber is provided with windows in the wall on opposite sides of the chamber which windows are transparent to the radiation. The radiation emitting means is located at one window and the radiation detecting means is located at the other window. In one preferred form, four windows are provided in the chamber wall with two radiation detecting means and two radiation emitting means so located at the windows that the radiation beams extend across the chamber, preferably at right angles to each other.
In a most preferred embodiment, six windows are provided in the chamber wall equally spaced from each other. Three radiation emitting devices are located at three of the windows and three radiation detecting devices are located at the other windows. The emitting and detecting devices are so located that the radiation beams extend at right angles to each other.
A movement detector having the two or more emitting and detecting means can be associated with electrical circuitry to firstly detect relative movement between the chamber and the body and secondly determine the extent and direction of acceleration of the chamber. The electrical circuitry receives signals from the detecting devices and compares the signals with the input to the emitting devices. The results of the comparison and then compared with each other and the circuitry is then able to determine whether or not there has been any change from an existing state and, if so, the rate and direction of change. The detector of the invention is therefore able to provide precise determination and calculation of movement of the body relative to the chamber.